This invention relates to inks, and, more particularly inks that are useful for printing on low adhesion backsize coatings.
Pressure-sensitive adhesive webs are well-established articles of commerce. In the form of tapes of varying width they are used to perform many functions including joining, mending, masking, sealing, splicing, protecting, reiforcing, identifying and decorating. Webs of larger width are often employed as coverings for walls and the like. A common procedure in handling a pressure-sensitive adhesive web is to wind it in a roll with adjacent contact between adhesive-coated and adhesive-free sides, the web being unwound thereafter before use. In order to faciliate unwinding such a roll, the adhesive-free side of the web is usually coated with an appropriate "low adhesion" or release coating, often called a low adhesion backsize or LAB.
In many applications of pressure-sensitive adhesive webs, it is desirable to have a printed message or design on the adhesive-free side of the web. When some commonly available inks are used for such printing, a difficulty is encountered which arises from the tendency of the print to transfer to the adjacent adhesive-coated side when the web is unrolled, particularly if the printed web is retained in roll form for prolonged periods of time or at elevated temperatures. When other commonly available inks are used, the adhesion of ink to the adhesive-coated side frequently is so strong that the web breaks when an attempt is made to unroll it. This is particularly the case when highly aggressive adhesives are used. In some instances adhesive separates from the adhesive-coated side and transfers onto the print. When it is attempted to overcome the aforementioned deficiencies by reducing the adhesive level of the pressure-sensitive adhesive, the usefulness of the product is seriously limited to applications which require only low bond strength. For example, adhesive tapes intended for reinforcing, joining or splicing would not be satisfactory if made in this manner.
Attempts have been made to modify the ink by the addition of natural or synthetic waxy materials, but such procedures have been unsatisfactory because such additives tend to migrate into the adhesive layer and cause a variety of deficiencies such as detackification and loss in adhesive and cohesive strength.
Another approach has been to subject the printed web, before rewinding, to an additional coating with an appropriate release agent but this involves cumbersome modifications in printing machinery and increased manufacturing costs.